Wide Area Networks (WANs) Slide Set 6

Wide Area Networks (WANs) Slide Set 6

Wide Area Networks (WANs) WAN Purposes Link sites (usually) within the same corporation Remote access for individuals who are off-site Internet access for individuals or firms SOBISE RHH 2

Wide Area Networks (WANs) Technologies for Individual Internet Access Telephone modems DSL lines / Cable modems Wireless Internet access Site-to-Site Transmission within a Firm Private line networks Public switched data networks (PSDNs) Virtual Private Networks (VPNs) Propagation over the Internet with added security Low cost per bit transmitted SOBISE RHH 3

Wide Area Networks (WANs) High Costs and Low Speeds High cost per bit transmitted compared to LANs Lower speeds (most commonly 56 kbps to a few megabits per second) Typical WAN speeds: 56 kbps to a few megabits per second. SOBISE RHH 4

Individual Internet Access: Telephone Modems

Telephone Modem Communication Computers are digital sources Telephone transmission lines are analog A modem converts between the two Digital Computer Signal Analog Signal Client A 56 kbps Modem Telephone SOBISE RHH 6

Telephone Modem Communication PSTN Digital Access Line Client A 56 kbps Modem Telephone ISP For 56 kbps Download Speed ISP Must Have a Digital Connection, Not a Modem SOBISE RHH 7

Digital Subscriber Lines (DSLs) DSLs provide data over the existing 1- pair voice-grade access line that already goes to residences and small businesses

Digital Subscriber Lines (DSLs) DSLs provide digital data transmission over the single-pair voice-grade local loop that already runs to residential customer premises. These lines are already installed, so no cost to run new access lines (as there is with private lines). Single-pair voice-grade UTP was not meant to carry data. Sometimes it works. Other times, it does not. Depends primarily on whether distance to the nearest end office is too far. SOBISE RHH 9

Digital Subscriber Lines (DSLs) Asymmetric DSL (ADSL) Asymmetrical throughput Downstream speed of 512 kbps to 1.5 Mbps Upstream speeds of 90 kbps to 384 kbps Good for Web access with large downloads Sufficiently fast for e-mail Aimed at residential customers Throughput is NOT guaranteed DSLAM (discussed later) often oversubscribed, slowing access SOBISE RHH 10

Digital Subscriber Lines (DSLs) Symmetric DSL Services Speed is symmetric Same upstream and downstream Aimed at business customers Throughput IS guaranteed Several Types of Symmetric DSL HDSL (768 kbps): Half of a T1 private line (later) HDSL2 (1.544 kbps): Full T1 private line speed SHDSL: Flexible (384 kbps to 2.3 Mbps) SOBISE RHH 11

Asymmetric Digital Subscriber Line (ADSL) Subscriber Premises PC Telephone ADSL Modem 2. Splitter 3. Downstream Data 512 kbps to 1.5 Mbps 4. Upstream 90 kbps to 384 kbps 1. Existing 1-Pair Voice-Grade UTP 5. Ordinary Telephone Service Telephone Company End Office Switch 6. DSLAM Data WAN PSTN SOBISE RHH 12

Wireless Access Systems Wireless Access to the Internet Fixed Versus Mobile Fixed For homes and offices (fixed locations) Use dish antennas Higher speeds Mobile People travelling within a city or farther Need omnidirectional antennas Lower speeds SOBISE RHH 13

Wireless Access Systems, Continued Satellite Versus Terrestrial Wireless Satellite Expensive because of transmission distance Expensive because satellites are expensive to launch and maintain Can cover large areas Terrestrial Earth-based radio stations Service within a city SOBISE RHH 14

Wireless Access Systems, Continued 802.16 WiMAX One of several terrestrial wireless access standards under development Fixed version being standardized first 20 Mbps up to 50 km (30 miles) Mobile version under development (802.16e) 3 Mbps to 16 Mbps for mobile users SOBISE RHH 15

Site-to-Site Networking: Private Line Networks

Private Line Networks for Voice and Data Connect sites via private lines Perspective User firm must do all the planning and installation User firm must operate and maintain the network Labour-intensive site-to-site networking SOBISE RHH 17

Private Line Networks for Data Site A Router Private Line Data Networks Have a Router at Each Site OC3 Private Line Site B 56 kbps Private Line Site D Site C T3 Private Line 56 kbps Private Line Site E T1 Private Line T1 Private Line 56 kbps Private Line SOBISE RHH 18

Private Line Speeds Trunk Line North American Digital Hierarchy 56 kbps (DS0 Signaling) T1 (DS1 Signaling) Fractional T1 Bonded T1s (multiple T1s acting like a single line) T3 (DS3 Signaling) *DG = Data Grade Speed 56 kbps (sometimes 64 kbps) 1.544 Mbps 128 kbps, 256 kbps, 384 kbps, 512 kbps, and 768 kbps Varies (usually up to 6 Mbps) 44.7 Mbps Medium 2-pair DG* UTP 2-pair DG* UTP 2-pair DG* UTP 2-pair DG* UTP Optical Fiber SOBISE RHH 19

Private Line Speeds, Continued Trunk Line Speed CEPT Multiplexing Hierarchy (Europe) 64 kbps 64 kbps E1 2.048 Mbps E3 34.4 Mbps Japanese Multiplexing Hierarchy 64 kbps 64 kbps J1 1.544 Mbps (same as U.S. T1) J3 32.1 Mbps SOBISE RHH 20

Private Line Speeds, Continued Trunk Line SONET/SDH* OC3/STM1 OC12/STM4 OC48/STM16 OC192/STM64 OC768/STM256 Speed 156 Mbps 622 Mbps 2.5 Gbps 10 Gbps 40 Gbps Notes: SONET and SDH speeds are multiples of 51.84 Mbps. (Figures listed are rounded off for readability) OCx is the SONET designation. STMx is the SDH designation. SOBISE RHH 21

Private Line Speeds, Continued Perspective Most the range of greatest demand for site-to-site transmission is 56 kbps to a few megabits per second So the largest market for private lines consists of T1 and fractional T1 lines or the equivalent in various countries SOBISE RHH 22

Site-to-Site Networking: Public Switched Data Networks

Private Line versus Public Switched Data Networks Site A Public Switched Data Network (PSDN) Site B POP Public Switched Data Network (PSDN) POP Point of Presence POP POP One private line per site Site D Site C Site E SOBISE RHH 24

Private Line versus Public Switched Data Networks Private Line Network Company must plan, buy switching equipment, and operate the network. Requires much labor. Public Switched Data Network PSDN carrier provides planning, switching, and operation of the network. This greatly reduces corporate management labor. PSDN drawn as a cloud to indicate that users do not need to understand it because the PSDN handles all of the details. SOBISE RHH 25

Virtual Circuit PSDN Switches Are Arranged in Meshes Loops so multiple alternative paths between stations Switches must consider alternative paths This is complex, making switching expensive SOBISE RHH 26

Virtual Circuit, Continued PSDNs Create Virtual Circuits Virtual circuit is a single path (data link) between two stations Set up before transmission begins Only a single possible path, so switching is fast and inexpensive Virtual Circuit Virtual Circuit SOBISE RHH 27

Virtual Circuit, Continued PSDNs Create Virtual Circuits Switching table has virtual circuit instead of data link layer addresses Frame header has a virtual circuit number, NOT a destination address Virtual Circuit A... B... C... D... Port 1 2 3 4 SOBISE RHH 28

Site-to-Site Networking: Frame Relay (FR) The most popular PSDN

Frame Relay (FR) The most popular PSDN Today Speed range is 56 kbps to up to 40 Mbps Matches main speed range of corporate WAN demand (56 kbps to a few megabits per second) FR Switching is Designed to Minimize Cost Switching is somewhat unreliable to reduce cost per frame Switching uses virtual circuits to reduce cost Cost minimization is important in WAN communication SOBISE RHH 30

Frame Relay Network Customer Premises A 1. Access Device Switch POP Customer Premises B Customer Premises C SOBISE RHH 31

Frame Relay Network, Continued CSU/DSU Channel service unit (CSU) protects the access line from unapproved voltage levels, etc. coming from the firm Data service unit (DSU) converts between internal digital format and digital format of access link to Frame Relay network. May have different baud rate, number of states, voltage levels, etc. DSU SOBISE RHH 32

Frame Relay Network, Continued Customer Premises A 2. T1 Private Access Line to POP Switch POP Customer Premises B Customer Premises C SOBISE RHH 33

Frame Relay Network, Continued Customer Premises A Switch POP 3. Port Speed Charge at POP Switch Customer Premises B Customer Premises C SOBISE RHH 34

Frame Relay Network, Continued Customer Premises A Switch PVC 2 PVCs 1&2 POP PVC 1 4. PVC Charges PVC 1 PVC 2 PVC 1 Customer Premises B Customer Premises C SOBISE RHH 35

Frame Relay Network, Continued Permanent Virtual Circuits (PVCs) Set up once, kept in place for months or years Between a firm s sites (which rarely change) The most common form of virtual circuit today Switched Virtual Circuits (SVCs) Set up at beginning of a communication session Taken down at the end of the session More expensive than PVCs, less common SOBISE RHH 36

Frame Relay Network, Continued Frame Relay Pricing Recap Frame relay access device at site (or router) Private line from site to POP Port on the POP Pay by port speed Usually the largest price component Permanent virtual circuits (PVCs) among communicating sites Usually the second-largest component of prices Other charges SOBISE RHH 37

Frame Relay Frame Variable Length Frames Start flag (01111110) to signal start of frame Address field has variable length (2-4 octets) Information field to carry data (variable) CRC (Cyclical Redundancy Check) field to detect errors (2 octets) If find errors, switch discards the frame Stop flag (01111110) to signal end of frame 01111110 Address Information CRC 01111110 SOBISE RHH 38

Frame Relay Frame, Continued Address Field of Frame Relay Frame Variable Length: 2-4 octets Usually 2 octets (as shown below) Data link control indicator (DLCI, pronounced dull -see) is the virtual circuit number (10 bits long in 2-octet form) Bits 0 7 DLCI (6 bits) C/R 0 DLCI (4 bits) FECN BECN DE 1 SOBISE RHH 39

Site-to-Site Networking: Asynchronous Transfer Mode: ATM

Asynchronous Transfer Mode: ATM ATM is a faster PSDN than Frame Relay Frame Relay: 56 kbps up to about 45 Mbps ATM: 1.5 Mbps up to 155 Mbps Not Competitors. Most PSDN Vendors Offer Both to Customers FR for low-speed customer needs ATM for higher speeds (at higher prices) As corporate demand grows, ATM may increase its market share SOBISE RHH 41

ATM Cell Fixed length (53 octets) frame allows simpler and therefore faster processing at switches For instance, switch does not have to do calculations to figure out how much buffer space it will need for a cell, as is the case with Frame Relay s variable-size frame. 53 Octets 5 octets of header 48 octets of payload (data) Fixed length frames are called cells. SOBISE RHH 42

ATM Cell, Continued Short Cell Length Limits Latency at Each Switch Switches may have to wait until the entire frame arrives before processing it and sending it back out. With shorter frames, there is less latency at each switch along the path Important in continent-wide WANs that require cells to pass through many switches Especially important for voice, which is highly latencyintolerant (ATM was created for digitized voice) SOBISE RHH 43

Site-to-Site Networking: Multi protocol Label Switching: MPLS

MPLS-Multi Protocol Label Switching MPLS is a data-carrying mechanism for both circuit-based and packet-switched clients. It can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, Frame Relay, and Ethernet frames. Router has two main elements Forwarding and routing Label switching is an alternative to IP forwarding MPLS (multi protocol label switching) combines benefits of virtual circuit with flexibility and robustness of datagram forwarding An MPLS-capable router uses traditional IP routing, but replaces IP forwarding with label switching. SOBISE RHH 45

Label Encoding SOBISE RHH 46

Flows, Trunks, LSPs, and Links SOBISE RHH 47

Site-to-Site Networking: Very Small Aperture Terminal: VSAT is a two-way satellite, ground station with a dish antenna that is smaller than 3 meters

VSAT VSAT can be used for data, voice, video or internet applications. It is used to communicate with or to link together locations using satellite connectivity. VSAT data rates typically range from narrowband up to 4 Mbps. A VSAT consists of two parts, a transceiver that is placed in direct line of sight to the satellite and a device that interfaces with the transceiver such as a PC. The transceiver receives or sends a signal to a satellite transponder in the sky. The satellite sends and receives signals from a ground station computer acting as a hub for the system. Each end user is interconnected with the hub station via the satellite, forming a star topology. The hub controls the entire operation of the network. For a user to communicate with another, each transmission has to first go to the hub station which then retransmits it via the satellite to the user's VSAT. SOBISE RHH 49

VSAT Illustration SOBISE RHH 50

Site-to-Site Networking: Metropolitan Area Ethernet Ethernet is moving into metropolitan area networks

Metropolitan Area Ethernet Ethernet is moving beyond the LAN Moving into the metropolitan area network (within a single urban area) New 802.3 standards (10 Gbps and 40 Gbps) being developed primarily for long distances of 10 km or more E-Line service: to connect LANs at two sites E-LAN service: to connect LANs at multiple sites Cheaper than ATM for high speeds Familiar technology so easy to manage Still lacks standards for carrier-class service New but growing rapidly compared to Frame Relay and ATM SOBISE RHH 52

Site-to-Site Networking: Virtual Private Networks: VPNs VPNs: Transmission over the Internet with added security

Virtual Private Network Issues Virtual Private Network (VPN) Transmission over the Internet with added security Some analysts include transmission over a PSDN with added security Why VPNs? Lower transmission cost per bit transmitted than PSDNs Adequate security SOBISE RHH 54

Virtual Private Network (VPN) 1. Site-to-Site VPN Tunnel VPN Server Corporate Site A Internet 3. Host-to-Host VPN VPN Server Corporate Site B 2. Remote Access VPN Remote Corporate PC SOBISE RHH 55

VPN Technologies SSL/TLS Limited to remote access VPNs SSL (Secure Sockets Layer) was its original name IETF changed it to Transport Layer Security Created to protect HTTP traffic in E-commerce Built into every browser and web server, so easy to implement Good if all traffic over the VPN will be HTTP Beginning to handle other protocols Moderate security SOBISE RHH 56

VPN Technologies, Continued Point-to-Point Tunneling Protocol (PPTP) For remote access VPNs Operates at the data link layer Transparently provides security to all messages at higher layers Software exists on all client PCs, but individual PCs must be configured to work with PPTP, and this is somewhat expensive Good for remote access when not all traffic is HTTP SSL/TLS has pushed PPTP almost entirely aside in the marketplace. SOBISE RHH 57

VPN Technologies, Continued IPSec For all types of VPN (remote access, site-to-site, host-to-host) Operates at the Internet layer Transparently protects traffic at all higher layers Very strong security Requires digital certificates for all computers Creating an infrastructure for certificates is expensive Installation and setup on individual client PCs is expensive SOBISE RHH 58

IPsec in Tunnel Mode Local Network IPsec Gateway Tunnel Mode IPsec IPsec Gateway Local Network Secure Tunnel No Security In Site Network Security Only Between Sites Hosts Need No Extra Software Only IPsec Gateways need Digital Certificates Easier to Set Up than Transport Mode No Security In Site Network SOBISE RHH 59

IPSec in Transport Mode Local Network IPsec Gateway IPsec Gateway Local Network Secure Tunnel Security In Site Network End-to-End (Host-to-Host) Tunnel Each Host Needs IPsec Software And Digital Certificate Security In Site Network SOBISE RHH 60